The invention relates generally to ion beam lithography and more particularly to proximity print type ion beam lithography capable of producing sub-50 nm feature size.
If microelectronics manufacturing is to continue its progress toward ever higher levels of performance and integration as well as lower cost per function, alternative lithographic techniques will be needed in order to resolve features of 50 nm and smaller. These techniques must offer high process throughput and reasonable cost per wafer. Many of the alternative lithography technologies explored thus far, such as X-ray, extreme-ultraviolet (EUV), electron-beam (e-beam), and ion-beam lithography, have been handicapped by complicated mask technology and/or low throughput.
The tremendous challenges associated with mask technology have provided incentive for exploring maskless approaches to lithography, such as the two different ones that are presently being investigated at the Lawrence Berkeley National Laboratory (LBNL). These two approaches could potentially have a revolutionary impact on the semiconductor industry. They are focused-ion-beam maskless direct-write lithography and masklesss ion beam projection lithography.
Focused ion beam (FIB) patterning of films is a well-established technique in semiconductor manufacturing (e.g., for mask repair), but throughput has historically been a prohibitive issue in its application to lithography. At LBNL a practical FIB system for high-throughput maskless and direct (resistless) patterning and doping of films is being developed. A compact FIB system using a multicusp ion source and a novel electrostatic accelerator column is being built to generate ion beams of various elements with final beam spot size <0.1 μm and current in the μA range for resist exposure, surface modification and doping. Incorporating a fast beam scanning technique in the accelerator column eliminates the need of a stencil mask and of resist. Parallel wafer processing with multiple beams can greatly enhance the throughput of a FIB system. A multiple-beam system can be built by stacking a multi-aperture electrode-insulator structure so that each beam is accelerated with the same electrode potentials. The FIB system is described in U.S. Pat. No. 5,945,677.
The Maskless Micro-ion-beam Reduction Lithography (MMRL) system takes a different approach than a conventional ion beam projection lithography (IPL) tool. The conventional IPL system needs a divergent beam from an ion source with very low energy spread. The beam is accelerated to 10 keV and is made parallel before impinging on a stencil mask. The stencil mask is a very thin membrane (˜3 μm thick) with open holes for beam passage. After exiting from the stencil mask, the beam is further accelerated and then demagnified to form a parallel beam again. The ion source, beam optics design and the stencil mask are extremely complicated and many engineering issues have to be resolved before a practical system can be realized. The MMRL system eliminates the first stage of the conventional IPL machine. The stencil mask is replaced by a patternable multi-beamlet system or universal pattern generator. The beam reduction column is all-electrostatic and has a much simpler design. The MMRL system is described in copending U.S. application Ser. No. 09/289,332.
While these two approaches both offer significant advantages, particularly the elumination of the stencil mask, they both involve accelerator columns, even though they may be more compact than conventional columns. It would be desirable to provide an ion beam lithography system which eliminates the need for an accelerator column to focus the ion beam and to reduce the feature size of a beamlet pattern produced by a universal pattern generator.